In lithography, there is an ongoing desire to reduce the size of features in a lithographic pattern in order to increase the density of features on a given substrate area. In photolithography, the push for smaller features has resulted in the development of technologies such as immersion lithography and extreme ultraviolet (EUV) lithography, which are however rather costly.
A potentially less costly road to smaller features (e.g. nanometer sized features, e.g., less than or equal to 50 nm, less than or equal 25 nm or less than or equal to 10 nm sized features) that has gained increasing interest is so-called imprint lithography, which generally involves the use of a “stamp” (often referred to as an imprint lithography template) to transfer a pattern onto a substrate. An advantage of imprint lithography is that the resolution of the features is not limited by, for example, the emission wavelength of a radiation source or the numerical aperture of a projection system. Instead, the resolution is mainly limited to the pattern density on the imprint lithography template.
Imprint lithography involves the patterning of an imprintable medium on a surface of a substrate to be patterned. The patterning may involve bringing together a patterned surface of an imprint lithography template and a layer of imprintable medium (e.g., moving the imprint lithography template toward the imprintable medium, or moving the imprintable medium toward the imprint lithography template, or both) such that the imprintable medium flows into recesses in the patterned surface and is pushed aside by protrusions on the patterned surface. The recesses and protrusions define pattern features of the patterned surface of the imprint lithography template. Typically, the imprintable medium is flowable when the patterned surface and the imprintable medium are brought together. Following patterning of the imprintable medium, the imprintable medium is suitably brought into a non-flowable or frozen state (i.e. a fixed state), for example by illuminating the imprintable medium with actinic radiation. The patterned surface of the imprint lithography template and the patterned imprintable medium are then separated. The substrate and patterned imprintable medium are then typically processed further in order to pattern or further pattern the substrate. The imprintable medium may be provided in the form of droplets on the surface of a substrate to be patterned, but may alternatively be provided using spin coating or the like.
In order to be able to accurately apply a pattern to imprintable medium provided on a substrate, it is desirable to be able to accurately align the imprint lithography template used to imprint that pattern with a specific area or part of the substrate. This may be necessary, for example, to achieve a desired overlay specification wherein, for example, a second imprinted layer and first imprinted layer should be precisely positioned with respect to each other to be able to obtain a functioning device. For this precise positioning of different layers with respect to each other it is important to be able to (repeatedly) accurately align the imprint lithography template used to imprint that pattern with a specific area or part of the substrate. Partial or coarse alignment may take place before the imprint lithography template is contacting (i.e. is in contact with) the imprintable medium. Final and fine alignment may take place when the imprint lithography template is imprinted into the imprintable medium, and before, for example, the pattern in the imprintable medium is fixed or frozen by, for example, exposure to UV radiation. Alternatively or additionally, coarse and/or fine alignment may take place during or after the time when the imprintable medium fills recesses and flows around protrusions of the imprint lithography template. Coarse alignment may be necessary before fine alignment can be performed, because the coarse alignment may bring the imprint lithography template and substrate alignment marks into a capture range of a fine alignment system. Fine alignment may not be possible if the imprint lithography template and substrate alignment marks are not in capture range of the fine alignment system.